JP2001203535A - Composite vibrator and voltage controlled piezoelectric oscillator using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a voltage controlled piezoelectric oscillator that is driven at a low voltage with a wide frequency variable range. SOLUTION: The composite vibrator consists of a piezoelectric substrate on which 1st and 2nd electrodes with different electrode areas are arranged and the other substrate on which a 3rd electrode is arranged and a relation of f1-f2≈f2-f3 and t1-t2≈t2-t3 is satisfied, where t1, t2, t3 are respective top temperatures of the vibrator configured with the 1st, 2nd and 3rd electrodes and f1, f2, f3 are frequencies at the respective temperatures.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage controlled piezoelectric oscillator, and more particularly to a low voltage driven voltage controlled piezoelectric oscillator having a wide frequency variable range.

[0002]

2. Description of the Related Art Piezoelectric oscillators using piezoelectric vibrators are widely used in communication equipment, electronic equipment, and the like because their frequency stability, frequency temperature characteristics, and frequency aging characteristics are superior to oscillators using other electronic components. It is used. However, in a piezoelectric oscillator using a single piezoelectric vibrator, for example, an AT-cut quartz vibrator, there is a frequency variation of 6 ppm to 7 ppm in a temperature range of -30 ° C. to 80 ° C., and a high-precision frequency source is needed as it is. It could not be used for communication devices that do. On the other hand, various temperature compensating means have conventionally been employed as means for stabilizing the frequency in the above-mentioned temperature range, but as a result, the variable range of the frequency has been narrowed, and a wide range required in recent oscillators for communication equipment has been widened. The frequency variable ability cannot be satisfied. Therefore, as a means for securing a certain degree of frequency stability, a composite vibrator in which three piezoelectric vibrators having quadratic curve temperature characteristics are connected in parallel has been proposed, for example, in Japanese Patent Publication No. 51-36154.

FIG. 10 is a diagram showing the structure of a temperature-compensated composite resonator. FIG. 10A shows a configuration in which three BT-cut crystal resonators Y1, Y2, and Y3 are connected in parallel, and a load capacitance C
_L is connected in series, FIG. 3B is an electrical equivalent circuit diagram, and FIG. 3C is a circuit diagram showing three BT-cut crystal units Y.
The frequency temperature characteristics of Y1, Y2, and Y3 are displayed with the horizontal axis representing temperature and the vertical axis representing frequency. Here, the peak temperatures of the three BT-cut quartz resonators Y1, Y2, and Y3 (the temperatures at which the first-order derivative with respect to the temperature becomes zero when the frequency-temperature characteristic exhibits a quadratic curve) are t1 and t, respectively.
2, t3, and the frequencies at that temperature are f1, f, respectively.
2, f3. According to the above publication, three BT-cut crystal units Y1, Y2 and Y3 are f3ｆf1, t3-t
When conditions such as 2 ≒ t2−t1 are satisfied, FIG.
It is described that the frequency-temperature characteristic of the composite oscillator becomes substantially flat. Further, by making the inductance L2 of the BT cut crystal resonator Y2 larger than the inductances L1 and L3 of the BT cut crystal resonators Y1 and Y3, when the load capacitance _CL is changed, the deterioration of the frequency temperature characteristic is minimized. It is noted.

[0004]

However, when a composite resonator is formed by using a BT-cut crystal resonator based on the above-mentioned publication, the frequency-temperature characteristic can be obtained over a wide temperature range. However, there is a problem that the crystal resonator is required and the structure becomes complicated, resulting in an increase in cost. Furthermore, when a VCXO is formed using the above-described BT-cut quartz crystal resonator, the frequency variable range is limited, and it is impossible to realize a wider range of variable capability.
On the other hand, in order to improve the above-mentioned frequency variable range, it is conceivable to configure a composite resonator using an X-cut lithium tantalate resonator in a thickness sliding vibration mode having a smaller capacity ratio γ than a BT-cut quartz crystal, Although the frequency variable range is improved, there is a problem that the frequency temperature characteristic is extremely deteriorated. For example, even with an X-cut lithium tantalate oscillator with an optimal energy confinement factor, B
The frequency-temperature characteristic of a T-cut crystal resonator is twice or more worse than that, and it is extremely difficult to achieve the purpose even if a composite resonator is formed using this. The present invention has been made to solve the above problem, and has a frequency-temperature characteristic of AT.
Superior to cut quartz crystal units, for example, the frequency variable range is A
It is an object of the present invention to provide a voltage-controlled piezoelectric oscillator that is as large as about four times the size of a T-cut crystal resonator.

[0005]

According to a first aspect of the present invention, there is provided a composite oscillator according to the present invention and a voltage-controlled piezoelectric oscillator using the same. Wherein the at least two opposing electrodes are arranged differently from each other, and the peak temperatures of the vibrators formed by the respective electrodes are different from each other. Claim 2
According to the invention described above, a first piezoelectric substrate in which a first counter electrode and a second counter electrode having an area different from that of the first counter electrode are arranged at a predetermined interval; and a third counter electrode. And a second piezoelectric substrate on which the first electrode, the second electrode, and the third electrode are formed. The peak temperatures of the oscillator formed by the first electrode, the second electrode, and the third electrode are defined as t1, t2, and t3, respectively. When the frequencies at the top temperature of the vibrator are f1, f2, and f3, respectively, f2-f1 ≒ f2-f3 and t2-t1 ≒ t3-t
2 is a composite vibrator characterized by being configured to satisfy 2. According to a third aspect of the present invention, there is provided the composite vibrator according to the first aspect, wherein the piezoelectric substrate is a Langasite substrate near the Y cut. According to a fourth aspect of the present invention, there is provided a voltage-controlled piezoelectric oscillator, wherein an oscillator is configured by connecting the composite resonator according to the first or second aspect, an amplifier and a variable capacitance element in series.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on an embodiment shown in the drawings. FIG. 1A is a diagram showing a configuration of a composite vibrator according to the present invention, which is a composite vibrator in which three Y-cut langasite (La ₃ Ga ₅ SiO ₁₄ ) vibrators are connected in parallel. (B) is an electrical equivalent circuit thereof. One feature of the present invention resides in that a Y-cut Langasite vibrator in a thickness-shear vibration mode is used for the piezoelectric vibrator. Y-cut Langasite vibrator capacitance ratio γ (ratio of capacitance C ₀ to motional capacitance C ₁ , γ = C ₀
/ C ₁ ) is about 60 and the capacitance ratio of AT-cut quartz resonator (25
Since it is much smaller than 0), when a composite vibrator is configured using the vibrator, the frequency variable range is expected to be considerably wide. The frequency temperature characteristic of the Y-cut Langasite vibrator is a quadratic curve convex upward, that is, Δf / f = a
(T−t _i ) ² + b (t−t _i ), and by connecting three vibrators in parallel, a composite vibrator having good frequency-temperature characteristics can be expected. Here, a is the secondary temperature coefficient, b is the primary temperature coefficient, and t _i is the peak temperature.

As described above, in order to develop a composite oscillator having good frequency-temperature characteristics and a wide frequency variable range,
Various experiments were performed using a cut Langasite oscillator. FIG. 2 shows that, when the temperature range of a composite vibrator in which three Y-cut Langasite vibrators are connected in parallel is set to, for example, a range of −35 ° C. to 85 ° C., the apex temperatures of the three vibrators and FIG. 4 is a diagram illustrating a resonance frequency at a peak temperature.
The center frequency is set to 20 MHz, and as shown in FIG. 2, the apex temperatures t1 of the Y-cut Langasite vibrators Y1, Y2, Y3,
t2 and t3 are set at −195 ° C., 25 ° C., and 245 ° C. at 220 ° C. intervals, so that the frequencies f1 and f3 at the peak temperatures of Y1 and Y3 are substantially equal, and the frequency f2 at the peak temperature t2 of Y2 is f1. 967 from f3
Set higher than ppm. Further, it is shown Y1, Y3 of the inductance L1, L3, respectively 2mH, Y2 8mH inductance L2 of the frequency temperature properties of the composite transducers and 3pF parallel capacitance C ₀ in FIG. The three curves are load capacity
Each 8 pF, 10 pF for C _L as a parameter, a case of setting to 12 pF, the frequency deviation is the largest C _L = 8p
Even at F, 7pp in the temperature range of -35 ° C to 85 ° C
m, which is almost the same value as in the case of the AT-cut quartz resonator, and it can be confirmed that the frequency temperature characteristic becomes almost flat when C _L = 10 pF.

[0008] Curve α shown in FIG. 4 is the load capacitance C _L is 8 pF,
It is a curve which shows the relationship between control voltage Vcont and frequency fluctuation (DELTA) f / f when changing the applied voltage of a variable capacitance element (varactor diode) to 3p, 2.5v, and 2v so that it may become 10pF and 12pF. For comparison, a control voltage-frequency variation curve β of the VCXO constituted by using the AT-cut quartz resonator was also overwritten. As is apparent from FIG.
Voltage sensitivity of VCXO using cut crystal oscillator is 133
ppm / V, the voltage sensitivity of a VCXO using a complex oscillator in which three Langasite oscillators are connected in parallel is 5
It can be seen that the frequency variable characteristic is 53 ppm / V, which is about four times as large.

FIG. 5 is a view showing the structure of a composite vibrator according to another embodiment of the present invention. FIG. 5A is a plan view showing the structure of three langasite vibrators Y1, Y2 and Y3. Figure,
(B) is a sectional view taken along the line QQ. Two of the three langasite vibrators Y1 and Y2 are the piezoelectric substrates 1
The counter electrodes 2a and 2b are disposed on the
a and 2b at positions where there is no acoustic coupling with the counter electrodes 3a and 3b
Are provided, the lead electrodes extend from the electrodes 2a, 3a and the electrodes 2b, 3b toward the ends of the substrate, and are connected to form lead electrodes 4a, 4b. Further, the opposing electrodes 6a and 6b are arranged on another piezoelectric substrate 5, and the lead electrodes 7a and 7b extend from the electrodes 6a and 6b toward the ends of the substrate, respectively, to form the piezoelectric vibrator Y3. Then, the piezoelectric substrates 1 and 5 are housed in a ceramic package 8 or the like, and the ends of the lead electrodes 4a, 4b, 7a, 7b and the terminal electrodes of the package are bonded and fixed using conductive adhesives 9, 9 to form a composite. Construct a piezoelectric vibrator. At this time, the cutting angles of the piezoelectric substrates 1 and 5 are generally made different.

The feature of this embodiment is that two piezoelectric vibrators Y1 and Y2 having different electrode areas are formed on the same piezoelectric substrate, and are housed in the same package together with the separately formed piezoelectric vibrating element Y3 to form a composite piezoelectric vibrator. That is, the child was constructed.
By configuring the composite piezoelectric vibrator in this manner, the number of expensive piezoelectric substrates can be reduced and the size can be reduced. Since a langasite substrate near the Y-cut is used for the piezoelectric vibrators Y1, Y2, and Y3, the vibration mode is thickness-shear vibration, and the frequency-temperature characteristic is a quadratic curve convex upward.

FIG. 6 shows a Y-cut Langasite substrate with 10
FIG. 9 is a diagram showing a relationship between an electrode area and a vertex temperature t _i when a 1000 ° gold electrode is attached to a 0 ° chromium base electrode so as to face each other. As is clear from the figure, even with a piezoelectric vibrator using the same cutting angle, it was found that the vertex temperature t _i moves to the lower temperature side as the electrode area gradually increases.
FIG. 7 shows the relationship between the electrode area of the piezoelectric vibrator and the primary temperature coefficient b. It can be seen from FIG. 7 that the primary temperature coefficient b decreases as the electrode area increases.

FIG. 8 is a diagram showing the relationship between the electrode area and the secondary temperature coefficient a. As is clear from this figure, it can be seen that the secondary temperature coefficient a hardly depends on the electrode area. 6, 7 and 8 show the relationship between the electrode area and the apex temperature t _i , the primary temperature coefficient b and the secondary temperature coefficient a experimentally with the electrode thickness kept constant. The size of the electrode and the electrode thickness, that is, the amount of frequency decrease Δ = (ff−
e) It is presumed that it depends on the product of the square root of / fs (f: resonance frequency, fe: cut-off frequency of the electrode portion, fs: cut-off frequency of the substrate portion) (called the energy confinement coefficient). You.

The peak temperatures t1, t2, t3 of the three piezoelectric vibrators Y1, Y2, Y3 and their respective frequencies f1, f2,
The relationship with f3 is set based on the above publication as shown in FIG. As shown in FIG. 5, three piezoelectric vibrators Y1,
Two oscillators whose peak temperatures are adjacent to each other among Y2 and Y3,
For example, Y1 and Y2 may be formed on the same langasite substrate. At this time, by reducing the electrode area of Y2 based on FIG. 6, the interval between the peak temperatures t1 and t2 of Y1 and Y2 can be appropriately set. The peak temperature t3 of Y3 can be freely determined by appropriately selecting the cutting angle. Further, by setting the apex temperature t2 of the piezoelectric vibrator Y2 at an intermediate value between t1 and t3, the inductance L2 of Y2
Since it is also possible to increase than others, there is an advantage that deterioration can also be minimized in the frequency temperature characteristics in a case where varying the load capacitance C _L.

In the above, the case where a Langasite substrate near the Y-cut is used as the piezoelectric substrate and two piezoelectric vibrators are formed on the substrate has been described. However, the present invention is not limited to this. A plurality of vibrators are formed on the same piezoelectric substrate such as a piezoelectric material, for example, lithium tetraborate, so that the respective peak temperatures and the respective frequencies at those temperatures are different from each other to form a composite piezoelectric vibrator. A voltage-controlled piezoelectric oscillator may be configured by using this.

[0015]

As described above, according to the present invention, a plurality of vibrators are formed on a langasite substrate in the vicinity of the Y-cut, and the peak temperature of each vibrator is made different to make a composite piezoelectric vibrator. It is possible to configure children.
If a voltage-controlled piezoelectric oscillator is configured using the composite vibrator, the frequency-temperature characteristic can be made to be approximately the same as that of an AT-cut quartz-crystal vibrator, and a voltage-controlled piezoelectric oscillator with much higher frequency variable sensitivity can be realized. When the oscillator is used for a communication device or the like, an excellent effect that a device that can transmit data at high speed with low power consumption can be realized can be obtained.

[Brief description of the drawings]

FIG. 1A is a composite vibrator configured by connecting three Langasite vibrators in parallel, and FIG. 1B is an electrical equivalent circuit diagram thereof.

FIG. 2 is a diagram showing peak temperatures and frequencies of three Y-cut langasite vibrators.

FIG. 3 is a frequency temperature characteristic when a load capacitance C _L of a voltage controlled piezoelectric oscillator is used as a parameter.

FIG. 4 is a diagram showing a relationship between a control voltage Vcont of a voltage controlled piezoelectric oscillator and a frequency variation curve.

5A and 5B are diagrams showing a configuration of a composite vibrator according to another embodiment of the present invention, wherein FIG. 5A is a plan view of a composite piezoelectric vibrator, and FIG. 5B is a cross-sectional view thereof.

FIG. 6 shows two Y-cut Langasite vibrators and one Y
It is a figure which shows each vertex temperature of a cut Langasite oscillator, and those frequencies.

FIG. 7 is a diagram illustrating a relationship between an electrode area of a Y-cut langasite vibrator and a primary temperature coefficient.

FIG. 8 is a diagram illustrating a relationship between an electrode area of a Y-cut langasite vibrator and a secondary temperature coefficient.

FIG. 9 is a diagram illustrating peak temperatures and frequencies of three Y-cut langasite vibrators.

FIG. 10 is a diagram showing a configuration of a conventional composite piezoelectric vibrator.
(A) is a circuit diagram in which three piezoelectric vibrators are connected in parallel and a load capacitance is connected in series, (b) is an electrical equivalent circuit diagram thereof, and (c) is a peak temperature of each of the three piezoelectric vibrators. FIG. 3 is a diagram showing the frequency of the signal.

[Explanation of symbols]

1, 5 ··· piezoelectric substrate 2a, 2b, 3a, 3b, 6a, 6b ··· electrode 4a, 4b, 7a, 7b ··· lead electrode 8 ··· package 9 ··· conductive adhesive Y ₁ , Y ₂ , Y ₃ ·· Piezoelectric oscillator AMP ··· Amplifier D ··· Variable capacitance element L ₁ , L ₂ , L ₃ ··· Inductance C ₁ , C ₂ , C ₃ ··· Motional capacitance R ₁ , R ₂ , R ₃ ··· Equivalent resistance C _L ··· Load capacitance t ₁ , t ₂ , t ₃ ··· Vertex temperature f ₁ , f ₂ , f ₃ ··· Frequency at vertex temperature C ₀ ··· Parallel capacitance

Claims (4)

[Claims] 1. A composite vibrator in which at least two opposing electrodes having different areas are arranged on one piezoelectric substrate, and the peak temperatures of the vibrators formed by the respective electrodes are different from each other. 2. A first piezoelectric substrate in which a first opposing electrode and a second opposing electrode having an area different from the first opposing electrode are arranged at a predetermined interval, and a third opposing electrode. And a second piezoelectric substrate on which the first electrode, the second electrode, and the third electrode are formed. The peak temperatures of the oscillator formed by the first electrode, the second electrode, and the third electrode are defined as t1, t2, and t3, respectively. When the frequencies at the top temperature of the vibrator are f1, f2, and f3, respectively, f2-f1 ≒ f2-f3 and t2-t1 ≒ t3-t
2. A composite vibrator characterized by satisfying 2. 3. The composite vibrator according to claim 1, wherein the piezoelectric substrate is a Langasite substrate near the Y cut. 4. A composite vibrator according to claim 1 or 2,
A voltage controlled piezoelectric oscillator comprising an amplifier and a variable capacitance element connected in series to form an oscillator.